Light and electron microscopical analyses of cat, rat and human retinas will be done to determine the effects of aging on retinal neurons and Muller cells. It is proposed here to examine the retinas of inbred strains of Sprague-Dawley rats from the young adult to the old adult (28 months), of cats of known age, and of human retinas from donor eyes of known age. Morphometric analyses will include measurements of inner and outer segment length and diameter; interphotoreceptor spacing and the photoreceptor mosaic; photoreceptor density; determinations of synaptic densities in the IPL; as well as some ultrastructural studies including findings on the occurrence of autolytic vesicles, lipofucsin and glycogen deposition in the neural retina; and studies of phagosome distribution in the pigmented epithelium. Findings from the cat and rat will form the basis for studies in the human material as it becomes available.